The only forum member who can reliably advise you with Old Irish is Embarien, a fairly infrequent contributor. I see he visited the forum just a few days ago, but either he wasn't interested in this thread or didn't see it. There are a few things there which need correcting but I won't be able to do anything till Friday or Saturday.

Thank you, I look forward to your thoughts! And the comment about tAncaire - what makes the t required, I'm just wondering? I like to learn as I go. And is there a way to ping Embarien, possibly, in the event he didn't see it? All insights are welcome, I want to do this right rather than make a fool of myself and dishonor the language. Thanks again!

'The race of things' - an cine rudaí/cine na rudaí. This is a difficult one - I'm not a native speaker - so I suggest you wait for confirmation (it's fine grammatically, but it might not sound right to a native speaker. Bríd Mhór is our only n.s.).

'Rudalann': Where did you get this? It should be 'Rudlann' anyway, but as said previously, it doesn't work, though the thinking behind it is understandable.

'The place of Things': Tír na Rudaí (= 'The land of Things') which might just possibly be capable of being condensed to (An) Rudthír (= ('The) Thingland') - my own invention, might even flout a spelling rule, would definitely need confirming.

04 - '(cáin) lánunma': looks like the genitive or adjectival form. The nominative would probably be slightly different.

06 and 07: You asked why the t. It's a grammar thing. t- or t is prefixed to masculine nouns beginning with a vowel when preceded by the singular definite article an: an t-ardsagart - the high priest; ardsagart - a high priest (there's no indefinite article in Irish). As mentioned previously, if the first letter is a capital, then no hyphen - an tArdsagart

08 - Mingary: According to that St Michael's Church site, it's a Gaelic word meaning 'the quiet place'.It's obviously an anglicised form, but whether Scottish Gaelic (more likely) or Irish, old or modern, what word it might be - I don't know. It looks a bit like the English version of a Gaelic place-name, but there's no such place in Ireland, and though there's 'Mingary Castle' in the Gaelic-speaking Highlands of Scotland, it turns out that 'Mingary' is an anglicised version of the original Norse name.

09- 'forosnaí' : I see both imbas forosna and imbas forosnaí on various sites. I see also uair forosnaí. It all depends on its grammatical function. These forms might be genitive or adjectival. If you want the nominative on its own, it might well be different. I have no idea.

12 - Slane: Yes, it's a (proper) noun. An anglicisation of Sláine, the name of that well.

As has been said already, you have a nice mish-mash of Old and Modern Irish. To contact a forum member, click on his/her name - in a post made by him/her, say - which brings you into his/her profile. There's contact info there.